The invention relates to an apparatus for the periodical movement of glass panes dependingly fastened to carrier means through a heating oven, especially for the transportation of panes through the various stations of a glass toughening or tempering installation in which the carrier means are cyclically movable by a conveyor means extending over the entire transport path.
Apparatus of this kind, whose manner of operation is described, for example, in German "Offenlegungsschrift" 2,146,518, serve for the purpose of conveying the dependingly fastened glass panes through the various stations of the glass toughening installation -- for example, one comprising a single oven for the production of bent panes, in which a glass pane attaching station, an oven chamber, a bending station with a press, an air quenching station, and a glass pane removal or offbearing station are arranged in succession. The intervals between the individual stations must, of course, be of equal length and must correspond to one step of the periodical transport movement of the conveyor means, so that the glass panes suspended from the carrier means will arrive successively precisely at the correct point within the various stations. In the interest of preventing the glass preheated in the oven from cooling before it is introduced into the press, the distance between the oven and the bending station is kept as small as possible. If this distance were unnecessarily great, the result would be that particularly large, thin panes would cool to a disproportionately great extent in the outside air, since in this case the mass of the glass, and hence the amount of stored heat, is relatively low, so that the plasticity of the glass would no longer be sufficient for the mechanical forming thereof in the press (bending station).
The result of this, of course, is that the distance covered by the conveyor means in each individual step is adjusted to the distance between the oven and the press. The distance between the glass pane attaching station and the oven is generally greater than the distance between the oven and the bending station, so that a freshly appended pane does not enter right away into the oven, but during the first step, that is, the step during which a pane in the oven is being carried into the bending station and then into the air quenching station, it remains hanging ahead of the oven during the short stay of the preceding pane in the bending station, and it is not introduced into the oven until the preceding pane has been pressed and moves on.
Apparatus of the kind described above, in which the cycle of the conveyor means is adjusted to the distance between the oven and the bending station, have proven entirely effective in toughened-glass installations having a single oven chamber. However, in order to improve the uniformity of the heating of the panes and at the same time to enable them to be heated more rapidly, recourse has been taken to toughened-glass installations having a plurality of successively disposed oven chambers. When the conveying system described above is used, the disadvantage is now encountered that when, on the basis of the given cycle of the conveyor means, a fully heated pane is moved from the last oven chamber into the bending station and on into the air quenching station, the panes which are still hanging in the train of ovens have to be unnecessarily accelerated and decelerated again, which can result in oscillating movements due to the known problems involved in the hanging of the panes, with the disadvantageous consequences that result therefrom. Furthermore, such repeated acceleration and deceleration of the heated panes is also disadvantageous because the tongs which hold the panes then penetrate more deeply into the glass, resulting in the formation of "ears," or of starting points from which cracks may propagate later on. There is also the danger that the panes which are in the train of ovens may be left hanging briefly between two successive oven chambers during a step of the conveyor means corresponding to the movement of the pane in the last oven to the bending station, resulting in a loss of heat.
In like manner, problems occur even in toughened-glass installations for the production of flat glass when a plurality of oven chambers are used and panes of varying thickness are to be treated, requiring different periods of time in the individual oven chambers. The use of the known apparatus at a rhythm of movement of the panes through the toughened-glass installation which is determined by the movement of the conveyor means will then necessarily bring it about that, whenever the rhythm is set for the heating time required for panes of great thickness (approximately 50 to 60 seconds of heating time are required per millimeter of glass thickness), thin panes will remain too long in the oven, thereby becoming undesirably hot.